The purpose of this contract is to conduct a double-blind randomized trial to determine the efficacy of one or more acellular pertussis vaccines. Clinical trials of acellular pertussis vaccines are a top development priority for NIAID and for the PHS. NIAID has been delegated the authority to conduct efficacy trials for the National Vaccine Program (NVP), administrative locus of pertussis vaccine initiatives for the PHS, which will provide NIAID appropriated funds. A coordinated Phase I/II clinical trial (funded by NIAID) evaluating 13 candidate acellular pertussis vaccines for safety and immunogenicity was completed in June of 1991. The data collected from this trial will be used as a basis for recommending vaccine(s) to be used in the efficacy trial. The phase III trial, which has been Congressionally mandated, will be performed at a site outside the United States and will address many of the issues that were left unanswered in the efficacy trial performed in Sweden (1987-1989). Currently, sites have been developed in Canada, Italy and Sweden and final site(s) selection will be made by the US Government by September 1991. The study will involve up to two years of recruitment followed by two years of surveillance and monitoring for disease. Assuming normal circumstances, data on vaccine efficacy should be available in early 1996. Once safety and efficacy is demonstrated for one or more of these acellular vaccines, licensure for use in infants and children should follow quickly within the United States.